NeighborhoodAggregator

Features that leave this transformer will have only the group-by attributes present on them. Any other feature attributes are lost.

Process At End (Blocking): This is the default behavior. Processing will only occur in this transformer once all input is present.

Process When Group Changes (Advanced): This transformer will process input groups in order. Changes of the value of the Group By parameter on the input stream will trigger processing on the currently accumulating group. This may improve overall speed (particularly with multiple, equally-sized groups), but could cause undesired behavior if input groups are not truly ordered.

Considerations for Using Group By

There are two typical reasons for using Process When Group Changes (Advanced) . The first is incoming data that is intended to be processed in groups (and is already so ordered). In this case, the structure dictates Group By usage - not performance considerations.

The second possible reason is potential performance gains.

Performance gains are most likely when the data is already sorted (or read using a SQL ORDER BY statement) since less work is required of FME. If the data needs ordering, it can be sorted in the workspace (though the added processing overhead may negate any gains).

Sorting becomes more difficult according to the number of data streams. Multiple streams of data could be almost impossible to sort into the correct order, since all features matching a Group By value need to arrive before any features (of any feature type or dataset) belonging to the next group. In this case, using Group By with Process At End (Blocking) may be the equivalent and simpler approach.

Note: Multiple feature types and features from multiple datasets will not generally naturally occur in the correct order.

As with many scenarios, testing different approaches in your workspace with your data is the only definitive way to identify performance gains.

These parameters, measured in ground units, divide the input space into cells. The result is a grid of cells that expands in all directions from the origin (0,0). The center of the bounding box of each input feature is used to determine the cell for the feature. Once all input features have been read, an aggregate feature is created from all features in each cell. If linear features are input, they will have pseudo nodes removed from within their cells to further reduce the number of separate entities. No such reduction is done to any polygons or donuts that enter.

Note: To view the grid of cells that is created from these parameters, use the 2DGridCreator. Specify 0,0 for Starting X Coordinate and Starting Y Coordinate, respectively, and the same values for Column Width and Row Height as Neighborhood Width and Neighborhood Height, respectively.

When you set this parameter, neighborhoods with fewer than the specified number of features are merged with a vertical neighbor area in order to increase the number of members. You can prevent this from happening by setting the parameter to 0 (zero).